1. Field of the Invention
The present invention generally relates to a reversible thermosensitive coloring composition and a thermosensitive recording medium using thereof, and more particularly to a reversible thermosensitive coloring composition and a thermosensitive recording medium using thereof in which a coloring reaction between an electron donating chromophoric compound and an electron accepting compound is utilized.
2. Description of the Related Art
Currently, a reversible thermosensitive coloring composition which is easily colored and decolorized repeatedly has been developed.
In such a reversible thermosensitive coloring composition, a coloring reaction and a decolorizing reaction between an electron donating chromophoric compound (hereinafter, referred to as a chromophoric agent or leuco dye) and an electron accepting compound (hereinafter, referred to as a developer) are utilized. For example, Japanese Laid-Open Patent Application No. 5-124360 discloses that an organic phosphoric acid compound, a fatty carboxylic acid oxide or a phenol compound can be used as the developer. Japanese Laid-Open Patent Application No. 6-210954 discloses a phenol compound having a specific long chain fatty group hydrocarbon as the developer. These compounds enable the coloring and the decolorizing by controlling a temperature.
However, the reversible thermal recording medium utilizing the reversible thermosensitive compound is not suitable for use when exposed by light. When the colored recoding medium is exposed by light, a color concentration thereof is not decreased to that of a blank zone even if the decolorizing process is conducted by heating. That is, problems exist in light-resisting characteristics in that the decolorizing is not adequate, the color appearance is changed or the decolorized blank zone gets colorful.
We have proposed in Japanese Laid-Open Patent Applications Nos. 6-1066 and 6-155907 that an antioxidant or guanidine derivatives should be added to the recording layer in order to improve light-resisting characteristics. However, by an addition of such additive, an adequate decolorizing cannot be obtained. Further, an excess amount of such additive adversely influences the coloring after exposure. Moreover, the light-resisting characteristics are generally required to be improved.